In the development of an electrostatic latent image, the electrostatic latent image formed on a photosensitive member electrostatically adsorbs a frictionally charged toner.
As the conventional method for giving a toner electric charges, the developing method of two-component system is publicly known, in which a toner is mixed with a carrier, and stirred therewith, thereby being electrically charged . In one-component system, a toner is rubbed with a developing sleeve, a toner controlling blade, or a photosensitive member, thereby being electrically charged. In either of these methods, if the toner is not electrified evenly, there cause disadvantages in the developing and transferring steps. For this reason, in the conventional method for charging a toner with static electricity, the toner is incorporated with a charge-giving agent for giving the toner charges opposite to those of the carrier or the blade member. For example, a toner obtained by the pulverizing method is produced by mixing a charge-giving agent with a thermoplastic resin and a colorant, and kneading, pulverizing the obtained mixture, followed by classifying the obtained particles. In the suspension polymerized toner, a colorant and a charge-giving agent are dispersed into monomers, and they are polymerized to obtain a toner. In the capsule toner, a charge-giving agent is mixed with a colorant, and a substance of a low softening point such as a wax or the like, or with a liquid containing a fixing resin, and the obtained mixture is enveloped with a layer (serving as a capsul) of a higher softening point than that of each component of the above mixture. Furthermore, the Laid-Open Japanese Patent Publication No. 210368/1986 discloses a method in which the spherical resin particles of a negligibly small diameter, a binding resin, and a colorant are mixed and stirred at a temperature lower than the softening point of the spherical particle of the resin, and higher than the softening point of the binding resin, so that the colorant is adhered to the spherical particle of the resin by the aid of the fused binding resin. Still furthermore, the Laid-Open Japanese Patent Publication No. 37553/1984 discloses another method in which a colorant is adhered to the particle surface of a resin.
It is to be noted that in any of pulverized toner, suspension polymerized toner, capsul toner and the like, the charge-giving agent is present inside the obtained toner particle, however few is present on the surface of the particle. For this reason, the charge distribution of the toner becomes large resulting in problems of flying and fog of the toner. Furthermore, in the pulverized toner or capsul toner, whether or not each component of toner is dispersed homogeneously affects the variability of the charge distribution over the toner. Therefore, it becomes an important subject to homogeneously disperse each of components of toner.
Though the Laid-Open Japanese Patent Publication No. 210368/1986 discloses a toner, this toner also has the above-mentioned problems, because the surface of the toner particle is coated with a binding resin of a low softening point. Furthermore, in the toner disclosed in the Laid-Open Japanese Patent Publication No. 37553/1984, a colorant is adhered only to the surface of the toner particle, so that the image density or ID becomes low due to the shortage of colorant; however, the addition of a large amount of colorant causes the flake of colorant from the toner particle, and the flaked colorant is adhered to the surface of carrier, or is mixed with the developer, resulting in deterioration in copying resistance.
Especially, when a color toner is produced according to the conventional pulverizing method or spray-drying method, the colored charge-giving agent conventionally used for a black toner is required to be added in a certain large amount so as to give sufficient charges to the toner, which causes turbidity in color, resulting in an unsatisfactory color image.
The recent attention is paid to a colorless or light-colored charge-giving agent for a color toner such as phenothiazine compound as is disclosed in the Laid-Open Japanese Patent Publication No. 20485/1984; however, this agent has a problem of unstability in environment resistance, build-up time of electrification, or electrifying properties during copying operation, therefor not meeting the requirements of a toner.
Furthermore, a color toner containing, as a functional group of a resin, a polar group such as an amino group useful for improving charge-giving properties is proposed, for example, in the Laid-Open Japanese Patent Publication No. 3648-1985; however, it has also a problem of unstability in environment resistance, electrification-build-up time, and electrifying properties during copying operation, therefor not meeting the requirements of a toner.
The object of the present invention is to provide a stable color toner for developing an electrostatic latent image, which hardly flies about or spills on a copying sheet, and is superior in long-period electrification stability, environment resistance, and further quick in electrification build-up time, thereby overcoming the afore-mentioned problems. Another object of the present invention is to provide a color toner capable of reproducing a clear color image without any turbidity.